In recent years, the high integration and growing in size of semiconductor devices have been promoted, and thus, it has been demanded to make thinner and smaller encapsulation resin packages. With such demands, it has been desired to form the surface-protective layers and interlayer dielectric films of semiconductor devices and the redistribution layers of semiconductor packages, using materials having more excellent electric properties, heat resistance, mechanical properties, etc. Polyimide resin is one of materials capable of satisfying such requirements, and for example, the use of photosensitive polyimide, in which photosensitive properties are imparted to a polyimide resin, has been considered. The use of such photosensitive polyimide is advantageous in that a pattern formation step is simplified and a complicated production process can be reduced (see, for example, Patent Literatures 1 and 2).
A film of polyimide resin is formed by making a thin film from a solution (what is called varnish) of a polyimide precursor (polyamic acid) obtained by reacting tetracarboxylic acid dianhydride with diamine according to a method such as spin coating, and then performing thermal dehydrative ring closure on it (see, for example, Non Patent Literature 1). A polyamide resin is hardened through such dehydrative ring closure processes.
However, the conventional polyimide resin, in which a polyimide precursor is used, is problematic in that volume shrinkage is caused by dehydration (imidation) when it is hardened, and in that the loss of a film thickness and a decrease in size precision occur. In addition, it has been recently desired to carry out a film formation process at a low temperature, and thus, it has been desired to develop a polyimide resin, in which dehydrative ring closure can be carried out at a low temperature, and in which the physical properties of a film obtained after the dehydration and the ring closure are equivalent to those of a film obtained by carrying out dehydrative ring closure at a high temperature. However, since imidation becomes insufficient if a polyimide precursor is hardened at a low temperature, the physical properties thereof are decreased such that the formed cured film becomes fragile.
On the other hand, photosensitive resins, which do not need dehydrative ring closure, differing from the polyimide precursor, and which use other polymers having high heat resistance, have been studied (see, for example, Non Patent Literature 2 and Patent Literatures 3-7). In particular, in recent years, from the viewpoint of reduction of environmental impact, it has been desired to develop a positive tone photosensitive composition, which can be developed in an alkaline aqueous solution and can form a pattern with high heat resistance, for the intended use as a redistribution layer for semiconductor packages, etc.